/*
 * Copyright (c) 2001, 2003, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
 *
 *
 *
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 */

package com.sun.corba.se.impl.orbutil;

import java.util.EmptyStackException;

// We implement a Stack here instead of using java.util.Stack because
// java.util.Stack is thread-safe, negatively impacting performance.
// We use an ArrayList instead since it is not thread-safe.
// RequestInfoStack is used quite frequently.
public class StackImpl {

  // The stack for RequestInfo objects.
  private Object[] data = new Object[3];
  private int top = -1;

  // Tests if this stack is empty.
  public final boolean empty() {
    return top == -1;
  }

  // Looks at the object at the top of this stack without removing it
  // from the stack.
  public final Object peek() {
    if (empty()) {
      throw new EmptyStackException();
    }

    return data[top];
  }

  // Removes the object at the top of this stack and returns that
  // object as the value of this function.
  public final Object pop() {
    Object obj = peek();
    data[top] = null;
    top--;
    return obj;
  }

  private void ensure() {
    if (top == (data.length - 1)) {
      int newSize = 2 * data.length;
      Object[] newData = new Object[newSize];
      System.arraycopy(data, 0, newData, 0, data.length);
      data = newData;
    }
  }

  // Pushes an item onto the top of the stack
  public final Object push(Object item) {
    ensure();
    top++;
    data[top] = item;
    return item;
  }
}
